In listening devices of this kind it is a problem that the microphones need to be closely matched in order for a possible directional computational algorithms to function optimally. In order that the microphones stay matched over a long period, an automatic matching process is introduced. Here the signals from the microphones are continually analysed to ensure that over time there is no big difference in the output level from the microphones. In such listening devices it is also a problem that when the casing is accidentally touched or touched when applied to the ear, very loud sound output levels may be produced as the microphones are very sensitive to noise propagated through the material of the casing walls.
If substantial differences in the input to the microphones should occur, this might corrupt the outcome of the automatic matching process. Further, it has been discovered that such large differences are most likely to coincide with the occurrence of large and unpleasant noises which the user would prefer not to hear, like the noise which is produced when the casing is touched by the user. In hearing aids a large gain or amplification of the audio signal is introduced to compensate for the hearing loss of the user. This amplification amplifies all signals, wanted as well as non-wanted. The wanted signals usually originates some distance from the hearing aid and arrives travelling through the air. Noise from touching the hearing aid is very unpleasant since it results in a loud output signal from the hearing aid because of the frictional resistance, the banging from the acceleration of fingers etc. The noise increases as the origin of the noise moves closer to one of the microphones in a multi-microphone hearing aid.